How to adjust the brightness of a partial region

Through numerous graphics programs, I can easily change the brightness as well as the contrast level of a whole image. But sometimes I wish to be more specific in a certain area within the photo and do the adjustment only there. Haven't figured out how-to so far. Any tips?

I use GIMP, but if you know the answer in Photoshop, that's equally helpful. Thank you in advance.

What you need to do is first of pick a selection tool. Something like free-hand lasso or circle. Then adjust the feathering. The amount will depend on the size of the picture. Make a selection a little bigger than what you want lighted. The right click to go into the menu -> layer -> levels or curves.

Or you can make a selection and then go menu -> selection -> feather and then lighten